Turbocompressors are used in a variety of ways in industry and in power generation. For example, geared compressors are used for air fractionation in which oxygen and nitrogen from ambient air are separated from one another. For this purpose, an air compressor sucks in the filtered air and compresses it to the necessary pressure. The air is then cooled and fractionated into the main components, that is to say into nitrogen and oxygen as well as into a small proportion of noble gas. Compressor units then compress the oxygen and nitrogen in order, for example, to feed them into a line system for further use.
During the compression of oxygen, lubricant oil for the bearings of the compressor rotor and the delivery medium oxygen have to be carefully separated from one another because of the risk of explosion. For this reason, a labyrinth gasket, in particular a multi-chamber gasket, is usually arranged between a bearing and an impeller wheel which brings about the compression in order to separate the gas and in order to maintain the process-side pressure.
As a result of the cooling and subsequent fractionation of the air, the impeller wheel of the turbocompressor is subject to very low temperatures of below −30° C. In other gas separation processes, temperatures below −150° C. can be reached. In order to avoid brittle fracture behavior at such low temperatures, materials which are tough at subzero temperatures have to be used for the manufacture of the impeller wheel. If low temperatures are implemented in a geared compressor, not only the impeller wheels but also the rotor shaft have to be protected against brittle fracture within the seal-forming regions as far as the bearing points owing to the low operating temperature.
The impeller wheel or impeller wheels and the rotor shaft in the seal-forming region are usually fabricated from a high-alloyed steel which is tough at subzero temperatures in cold gas applications. For reasons of ease of manufacture and of mounting, the pinion shaft and impeller wheels are implemented separately. So that the pinion shaft or the rotor shaft satisfies stringent mechanical requirements in the toothing region, it is known to manufacture the pinion shaft from a material other than that of the impeller wheel or the hub thereof.
U.S. Pat. No. 1,808,792A, U.S. Pat. No. 3,874,824A, U.S. Pat. No. 1,853,973A and U.S. Pat. No. 5,482,437A have already disclosed compressors of the type defined at the beginning, which have a restricted suitability for operation at low temperatures.